Emission regulator



May 12, 1959 D. A. FLUEGEL ET AL 2,886,710

EMISSION REGULATOR Filed May 23, 1955 um mwN/vm IW K .mmv MNH/mm INVENTORS DA. FLUEGEL Mc. Bunn A ron ys United States Patent O frice EMISSIN REGULATOR Dale A. Fluegel and Marvin C. Burk, Bartlesville, Okla.,

assiguors to Phillips Petroleum Company, a corporation of Delaware Application May 23, 1955, Serial No. 510,192

Claims. (Cl. Z50-41.9)

This invention relates to current regulators. In another aspect, it relates to a mass spectrometer circuit whereby the filament emission current is maintained constant.

In mass spectrometers, it is very important that the filament emission current be kept constant so that a predetermined number of ions is produced per unit of time. Although various types of control devices have been proposed for regulating the filament current, difficulties are encountered in obtaining the necessary precise regulation, or it is necessary to provide rather elaborate circuits embodying special electrodes in the mass spectrometer tube.

In accordance with this invention, the direct current component of the filament voltage is sensed and compared with a standard potential to provide a resultant voltage which controls a saturab-le reactor connected in the primary circuit of the filament transformer. In this manner, a constant emission current is obtained despite variations in line voltage, changes in the characteristics of the filament, and other factors. Further, a novel comparison circuit is provided wherein the total cathode current of a dual tube in the comparison circuit is maintained constant, the saturable reactor control winding being included in the anode circuit of one section of this tube.v Finally, the reference voltage is derived from an impedance network of unique character, and it is electronically adjustable.

Although the present invention finds its primary application in mass spectrometers, it is useful in regulating the filament current of various types of tubes, and certain subcombinations of the invention have general applicability in the electronics field.

Accordingly, it is an object of the invention to provide a novel filament-control circuit for a mass spectrometer.

It is a further object to provide an improved current regulator.

It is a still further object to provide a novel regulating circuit for a voltage comparison unit.

It is a still further object to provide an impedance network of unique character.

It is a still further object to provide a circuit which is very accurate and reliable in operation, of low cost, and which utilizes a minimum number of standard circuit components.

Various other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure l is a schematic circuit diagram of a mass spectrometer constructed in accordance with the invention; and

Figure 2 is an equivalent circuit diagram of a portion of the circuit of Figure l.

Referring now to Figure l, We have shown a mass spectrometer tube having a filament 11, a collector electrode 12, a grounded shield electrode 13 together with a multiplicity of control electrodes including focus- 2,886,710 Patented May 12, 1959 ing elements 14, 15, five sets 16 of control electrodes, a set 17 of stopping electrodes and a set 18 of suppressor electrodes. Each set 16 of electrodes includes a central electrode 16a and all of the electrodes 16a are connected through an electronic switch 19 to an oscillator, not shown. Each set 16 further includes outer electrodes 1611 and 16C, and all of the electrodes 16b, 16C are connected through a resistance network 20 to a stepback rectifier and the aforementioned radio frequency oscillator. The stopping electrodes 17 are connected through a stopping detector 22 to the oscillator, and the suppressor grids 18, which repel secondary electrons, are connected to a negative terminal 23.

In operation, a sample material is introduced through an inlet 24, and ionized by electrons emitted from the filament 11. The resulting ions pass through the focusing elements 14 and 15. Ions of a predetermined mass are selectively accelerated as they pass through the sets 16 of control electrodes and the intervening field free drift spaces. Thus, ions of a predetermined mass are preferentially collected at the plate 12 and cause a voltage representative thereof to appear at the output terminals 25. An outlet 26 is provided which is connected to a pump to maintain a high vacuum continuously in the tube.

The operation of the tube and associated circuitry is described in greater detail in the copending application of M. C. Burk entitled, Ion Source, Serial Number 412,790, filed February 26, 1954, now Patent No. 2,792,500.

In order to obtain optimum results, it is necessary that the emission current of the filament 11 be accurately regulated. To this end, the filament 1l is connected to the secondary winding of a filament transformer 27. The primary winding of this transformer is connected to alternating current supply terminals 28 and 29 through a variable impedance 30 and one winding 31 of a saturable reactor 32 which has a second winding 33 controlling the amount of magnetic flux in the core thereof and, thus, the series impedance of the winding 31. The reactor 32, accordingly, regulates the primary voltage applied to the transformer 27 and, thus, the filament voltage applied to the tube 10.

The center tap 27a is connected by a lead 34 to the control grid of a triode 35a forming one section of a dual triode 35, and this lead is further connected through a meter 36 and a variable resistance 37 to a supply terminal 38 of an impedance network 39.

This impedance network includes two branches connected between a grounded lead 4f) and a lead 41 more negative than ground which is connected to a negative terminal 42, The first branch of the network includes four series-connected resistances 43, 44, 45 and 46 while the second branch includes two series-connected resistances 47 and 48. A fixed resistance 49 has one terminal connected to the junction between the resistances 45, 46 and its other terminal connected to the junction between the resistances 47 and 48.

An electron tube 50 has its cathode connected to the junction 45a between resistances 45, 46 and its anode connected to the lead 40. The control grid of this tube is connected to the contactor of a potentiometer 51 which, together with fixed resistances 52 and 53, forms a voltage divider connected between the leads 40 and 41. The network 39 further includes a terminal 54 at which a reference voltage is generated.

In the network 39, the voltage at terminal 54 is a predetermined fraction, as determined by the values of resistances 43, 44 and 45, of the voltages appearing at junction 45a. Moreover, the potential at terminal 38 is equal to the potential at terminal 54 plus a predetermined voltage determined by the values of resistances 47, 48

Ohms

The potential at lead 40 was zero volts and the potential at lead 41 Was minus 600 volts. With this arrangement, the voltage at junction 45a was three times the voltage at terminal 54, and the voltage at terminal 38 was ten volts lower than the potential at terminal 54.

It will be noted that resistance 44 is actually a potentiometer which has its contactor connected by a lead 55 to the focusing element 15. The focusing element 14 is connected to the contactor of a potentiometer56, one fixed terminal of which is connected to negative terminal 42, the other fixed terminal being grounded. In this manner, the voltage applied to the rst focusing element is varied as the reference voltage appearing at terminal 54 is changed so that a very advantageous lfocusing action is obtained.

ln accordance with the invention, the reference voltage appearing at terminal 54 is compared with the voltage at center tap 27a to produce a resultant voltage which controls the saturable reactor 32.

To this end, terminal 54 is connected by a lead 58 to the control grid of a triode section 35b. The cathodes of triode sections 35a, 35]; are interconnected and extend through a fixed resistance 59 to the negative terminal 42. The anodes of triode sections 35a, 35b are connected through resistances 60 and 61, respectively, to a lead 62 which, in turn, is connected through a fixed resistance 63 to a positive power supply terminal 64. These anodes are further connected to the respective control grids of a pair of triode sections 65a, 65b, forming a part of a second dual triode 65. The cathodes of this unit are connected to ground through a fixed resistance 66. The anode of section 65b is connected by a lead 67 and a fixed resistance 68 to the positive terminal 64 while the anode of section 65a is connected to the lead 67 through the second or control winding 33 of the saturable reactor 32.

'Ihe direct current circuit for regulating the emission current can be traced from the negative terminal 42 through the bridge 39, terminal 3S, resistance 37, meter 36, center tap 27a, and filament 11 to ground at the grids adjacent the filament, changes in emission current changing the Voltage drop across resistance 37 and thus the potential at the control grid of the tube 35a.

When equal voltages are applied to the control grids of triode sections 35a, 35b, lit will be evident that equal potentials are applied to the control grids of triode sections 65a, 65b and the anodes of these tubes are at the same potential with the result that equal currents flow through these tubes. It wi-ll further be evident that this condition prevails when the voltage at the center tap 27a is equal to the reference voltage at terminal 54.

However, should the voltage at center tap 27a vary from the reference voltage, a resultant voltage is developed in the anode circuits of triode sections 65a, 65b, changing the current flow in the control winding of reactor 33. This varies the impedance in the primary winding circuit of transformer 27. Thus, the primary voltage is changed by the action of the reactor 32 until the potential at the center tap 27a is again equal to that at terminal 54.

Under these conditions, it will be further evident that the emission current of the filament 11 is maintained constant and is controlled by variable resistance 37 independently of the voltage at center tap 27a. This can be better understood in connection with the simplified circuit diagram of Figure 2. It will be recalled that a predetermined reference voltage E is produced at terminal 54 which is represented in Figure 2 by a battery 54a having a potential of E volts. Moreover, the potential at supply terminal 38 differs by a predetermined voltage from that at terminal 54 which can be shown as a battery 38a and a fixed resistance 38b representing the equivalent impedance of the network 39. With the constants previously given for the impedance network, the potential of battery 38 is E minus ten volts, and the equivalent resistance of the network 38h is 8330 ohms.

Accordingly, when the potential at 27a is maintained equal to the potential at 54 by the action of the described regulating circuit, the emission current is equal to where X is the ohmic value of variable resistance 37 (which was a 300,000 ohm resistor in one practical embodiment). rlhus, the emission current is controlled solely by the values of resistances 37 and the network Iimpedances represented by resistor 38h. It is independent of the potential E due to the action of the described regulating circuit.

It will be seen that the control circuit of the invention has important advantages in that the emission is regulated without the necessity of measuring the voltage or current within the tube 10. Moreover, through the network 39, a very precise control can be obtained and a very steady electron flow maintained from the filament with resulting important advantages in the ionization of the sample material within the tube and measurement of the resulting ion current.

It is a further feature of the invention that the total current through the dual triode 65 is maintained constant and independent of supply voltage 64 variations, thus providing an improved regulating action. To this end, a third dual triode 70 is provided having sections 70a and 7Gb. The cathodes of both triode sections are grounded at 71 while the anodes are interconnected and extend through a lead 72 to the lead 62. The control grid of triode section 70a is connected through a fixed resistance 73, which can have a value of 470 ohms, to the control grid of triode sections 70b which, in turn, is connected through a fixed resistance 74 to the negative terminal 42 and through a fixed resistance 75 to' the cathodes of dual triode 65. Resistances '74 and 75 can have values of 6.8 megohms and 560,000 ohms, respectively.

`The triode 70 represents a variable impedance connected between lead 62 and ground, the tube impedance being controlled by the cathode potential of Kdual triode 65. Accordingly, dual triode 70 regulates the total cathode current of dual triode 65 by controlling the anode voltage applied to the triode sections 35a and 35b, a portion of this regulated current passing through the control winding 33 of reactor 32.

While the invention has been described in connection with a present, preferred embodiment thereof, it is to be understood that this description is illustrative only and is not intended to limit the invention.

We claim:

l. In a mass spectrometer, an evacuated tube including a filament, a pair of focusing electrodes, a collector plate, and a multiplicity of control electrodes, means for intr0- .assegno ducing material to be tested into said tube, means for applying alternating potentials to said control electrodes to cause ions of a selected mass to be preferentially transmitted to said collector electrode, a filament transformer having a center-tapped secondary Winding connected to said filament and a primary winding, a saturable reactor having a first winding connected in series with said primary winding and a second winding controlling the magnetic flux in said reactor, means for supplying an alternating current to said primary winding through said first winding of the saturable reactor, an impedance network connected between ground and a point of low potential, said network having a reference voltage terminal and a supply terminal where the voltage differs by a predetermined amount from said reference voltage, a vacuum tube having at least an anode, a cathode and a control grid, means connecting the anode and cathode of said tube in circuit with an impedance of said network so that changes in impedance of said tube vary the potential at said reference terminal and said supply terminal, means for varying the potential applied to said control grid so as to vary the voltage at said reference terminal and said supply terminal, a pair of potentiometers connected in parallel between ground and a terminal of said network where the voltage varies in accordance with changes in impedance of said vacuum tube, leads connecting the contactors of said potentiometers to the respective focusing electrodes, means connecting said supply terminal to said center tap, means for comparing the voltage appearing at said center tap with the voltage at said reference terminal to produce a resultant voltage, and means for controlling the flow of current through said second winding of the saturable reactor in accordance with said resultant voltage.

2. An emission regulator for a vacuum tube having a filament which comprises, in combination, a filament transformer having a center-tapped secondary winding connected to said filament and a primary winding, a saturable reactor having a winding connected in series with said primary winding, and a second winding controlling the flux in the core of said reactor, means for supplying alternating current to said primary winding and the series connected reactor winding, an impedance network arranged to produce a reference voltage and a supply voltage equal to said reference voltage plus a predetermined voltage, an electron tube connected in circuit with an impedance in said network so that changes in impedance of said tube vary said reference voltage and said supply voltage, means for varying the potential applied to a control electrode of said tube so as to vary the impedance thereof, a variable resistor connecting said center tap with said network at the terminal where said supply voltage is generated, means for comparing the voltage appearing at said center tap with said reference voltage to produce a resultant voltage, and means for applying to said second winding of the saturable reactor a voltage controlled in accordance with said resultant voltage so as to maintain said resultant voltage at a predetermined value.

3. An impedance network arranged to produce a reference voltage and a supply voltage equal to said reference voltage plus a predetermined voltage, an electron tube connected in circuit with an impedance in said network so that changes in impedance of said tube vary said reference voltage and said supply voltage, means for varying the potential applied to a control electrode of said tube so as to vary the impedance thereof, a transformer having a center-tapped secondary winding, a load connected to said winding, a saturable reactor connected in series with the primary winding of said transformer, said reactor having a control winding, first, and second dual triodes, a third triode means for supplying operating potentials to the electrodes of said triodes, leads connecting the control grids of said first dual triode to said center tap and to the terminal of said network at which said reference voltage appears, respectively, means coupling the control grids of said second dual triode to the respective anode circuits of said first dual triode, leads connecting said saturable reactor in the anode circuit of one section of said second dual triode, means connecting both anodes of said third dual triode to the anode voltage circuit of said rst triode, means coupling one control grid of said third dual triode to the cathodes of said second dual triode, and a xed resistance connecting together the control grids of said third dual triode.

4. An impedance network arranged to produce a reference voltage and a supply voltage equal to said reference voltage plus a predetermined voltage, an electron tube connected in circuit with an impedance in said network so that changes in impedance of said tube vary said reference voltage and said supply voltage, means for varying the potential applied to a control electrode of said tube so as to vary the impedance thereof, a control circuit including first and second dual triodes, a third triode means for supplying operating potentials to the electrodes of said triodes, leads respectively connecting the control grids of said first dual triode to two sources of voltage to be cornpared, means coupling the control grids of said second dual triode to the anode circuits of said first dual triode, respectively, leads connecting a controlled device in the anode circuit of one section of said second dual triode, means connecting the anode of said third dual triode to the anode voltage circuit of said first dual triode, and means coupling the control grid of said third triode to the cathodes of said second dual triode.

5. An impedance network including a direct voltage source, a first branch including first, second and third resistances connected in series across the terminals of said source, a second branch including a fourth and fifth resistances connected in series between the terminals of said source, a sixth fixed resistance having one terminal connected to the junction between said second and third resistances and its other terminal connected to the junction between said fourth and fifth fixed resistances, a terminal at the junction between said first and second resistances, a terminal at the junction between said fourth and fth resistances, an electron tube having at least an anode, a cathode and a control grid, a lead connecting the cathode of said tube to the junction between said second and third resistances, a lead connecting the anode of said tube to the positive terminal of said source, a voltage divider connected across said source, and a lead connecting the control grid of said tube with an intermediate terminal of said voltage divider.

References Cited in the file of this patent UNITED STATES PATENTS 2,436,822 Odessey Mar. 2, 1948 2,513,983 Winn July 4, 1950 2,544,716 Nier Mar. 13, 1951 2,813,978 Brenholdt Nov. 19, 1957 OTHER REFERENCES A Mass Spectrometer for Isotopes and Gas Analysis by Nier, published in Review of Scientific Instruments, v01. 18, No. 6, June 1947, pp. 398-411.

UNEEEO STATES PATENT OFFICE CERTIFiCATE 0F CORRECTION Non 58869710 May l27 1959 Dale A., Fiuegel et alo 1t is hereby certified that error appears in the-printed Specification of the above numbered patent requiring correction and that the Said Letters Patent should read as corrected below.

folunm op line 22 claim 39 after winding, :ih-Sert a variable feaiatoif connecting Said @enter tap with Said, network et the terminal where Supply Voltage iS geheated, ge; Same lille'y foi and Second. duel" :bead ma Second an@ third dual ma; column9 linea 2 and 3y out "e, third tiode line l2, foi Se-.ifi first t'fiode, read Signed alti Sealed this 8th day of December 1959o Attest:

ROBERT C. WATSON Attesting Gfcer Commissioner of Patents UNITED STATES PATENT OEETCE @ERTIHCATE OF CORRECTION Dale L, Eluegei et alo appears in the -printed specification correction and that the said Letters 1t is hereby certified that error of the above numbered patent requiring Patent should read as corrected below.

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